Home Phone Batteries
Cordless home phones are also known as DECT, Digitally Enhanced Cordless Telecommunications. They depend on their handset being able to communicate with their bases and this requires rechargeable battery power. Over time rechargeable batteries will weaken and eventually they'll need replacing.
Different battery types
Early cordless phones use NiCad, Nickel Cadmium batteries but these have largely been replaced with NiMH, Nickel Metal Hydride rechargeable batteries. Some of the latest cordless phones will have Li-Ion rechargeable batteries , but generally a cordless phone's battery will be NiMH. Each battery type has different charging characteristics and cannot be interchanged.
Battery Packs consist of several battery cells assembled into one unit and they have a protruding battery cable for connection to the handset. They are phone make and model specific and can only be replaced by the same type and specification. Doing this is easy, simply check the current handset battery pack and replace like for like. The same applies to Li-ion batteries.
AAA rechargeable batteries
Rechargeable batteries are available in different mAh capacities, milliampere per hour. The mAh rating is a measure of the amount of power a battery can hold and ranges from hundreds of mAh to thousands. Because of compatibility issues, it's not simply a case of getting the rechargeable battery with the highest mAh rating. The best rule of thumb is to check the original batteries in the handset and replace, as per battery packs, with exactly the same specification.
When to replace
Cordless phone battery performance is measured by stand by and talk time. Over time, twelve months or more, standby and talk time will noticeably reduce which is caused by the handset's batteries slowly losing their ability to charge and retain charge. At this point they will need replacing. If battery performance is too short for the age of the phone, try completely draining then recharging the batteries for 24 hours. If there is no improvement then they will need replacing.